Method and apparatus for making veneer



July 15, 1952 L. C. QUIMBY ET AL METHOD AND APPARATL I S FOR MAKINGVENEER Filed April 28, 1949 2 SHEET$SHEET l INVENTORS. M/vapo/v c 001MB)Hus/v 90mm y, l/R,

ML, N W T T p Patented July 15, 1952 METHOD AND APPARATUS FOR MAKINGVENEER Langdon C. Quimby and Allen Quimby, Jr., Bingham, Maine,assignors to Bingham Machine and Engineering Company, Bing-ham, Maine, acorporation of Maine Application April 28, 1949, Serial N 0. 90,114

15 Claims.

This invention relates to the production of wood veneer and specificallyto the drying thereof by continuously feeding a green veneer strip cuttangentially (widthwise of the grain) from a log and fed from a reelthrough a drying device in a direction widthwise of the grain andclipping the resulting dry veneer ribbon into individual dried sheets.

When veneer is cut from the log it is in a state in which the moisturecontent is above what is known as the fibre saturation point. As soon asthe moisture content drops below the saturation point in the drying ofthe veneer, contraction at right angles to the grain begins. The greenveneer as cut from the log and wound onto a reel has a low degree oftensile strength since its grain is at right angles to the length of thestrip, so that it is important in drying the strip to avoid anydestructive tensile stress lengthwise of the green veneer strip orribbon.

Heretofore, to prevent tearing or splitting of the veneer strip, veneerdrying methods have provided for drying without tensioning the veneerstrip widthwise of the grain by cutting the green veneer strip intorelatively small sheets that may be fed through a dryer. This dryingprocedure requires cutting of the veneer strip before drying (say intosheets about 3 to 8 lengthwise of the grain and a maximum of about 8Wide), and, since the warping and shrinkage will vary considerably fromsheet to sheet of apparently identical green veneer, it has been foundnecessary to provide considerable excess in the width of the greenveneer sheet to allow clipping the dry veneer sheets to a predeterminedsize. This results in considerable waste. Furthermore, since greenveneer is quite fragile, the necessary handling of the individual veneersheets causes considerable breakage and consequent waste, as they mustbe manually fed to the dryer from the green veneer clipper and thenagain manually fed to the final clipper before sorting and grading ofthe dry sheets.

The object of our invention is to permit the economical drying of therolled strip of green veneer as it comes from the veneer lathe bycontinuously passing the green veneer strip in a direction widthwise ofits grain through the drying device while applying a controlledlongitudinal tension uniformly across the entire width of the veneerstrip, and preferably a progressively increasing tension to the veneerstrip to reduce the amount of shrinkage, but still avoiding destructivetensile stress in veneer strips of considerable length, that is, twentyfeet or more.

A further object of our invention is to reduce warping and produceflatter, individual sheets of dry veneer by both drying and cooling theveneer strip while under tension on a substantially continuousunderlying moving support, and then removing the defects by clippingsuch defective portions from the veneer strip immedi.- ately upon therelease of tension so that such defects will not cause warping of theaccepted clipped veneer sheets during their further cooling in theuntensioned state, and also to obtain the required grade in the mostdesired size.

The advantages of our invention include a considerable increase inoutput by reducing "the shrinkage of the veneer strip, allowingapproximately 1% more dry veneer to be produced from the same amount ofgreen veneer as cut from the log, and, in addition, a reduction in, the.waste caused by the prior conventional han dling of the individual greenveneer sheets and the necessary allowance for shrinkage and warping inconventional drying methods requiring the cutting of the veneer stripinto relatively Small (though still oversize) sheets before dryinginstead of cutting the continuous dry veneer strip to final finishedsize according to our invention.

Another advantage of our invention results from the ready matching ofthe veneer sheets after clipping to size, since the grain pattern of theveneer strip will repeat at frequent intervals determined by thecircumference of the log (at the particular stage of cutting) and may bematched by picking up closely adjacent sheets of veneer as they emergefrom the clipper knife, thus again reducing the necessary handling andconsequent breakage of the thin veneer sheets.

Other advantages of our invention include a flatter product less subjectto warping, and a decreasre in the manufacturing costs by permittingcontinuous drying, cutting to final size, and ready matching of piecescut from the veneer strip as it comes from the log.

For the purpose of further explaining our in vention, reference is madeto the following drawings showing a preferred apparatus, in which:

Fig. 1 illustrates one form of apparatus suitable for use in carryingout the method of our invention;

Fig. 2 illustrates in graphical form the reduction in shrinkage lossresulting from drying typical birch veneer strips under varyingtensions, and

Fig. 3 illustrates the curves of Fig. 2 as extended to include theaverage dry birch veneer tensile strength.

Referring to Fig. 1, the continuous strip of veneer 2 as it comes fromthe log has been wound on a reel 4 at the cutting lathe, not shown. Thereel 4, placed on suitable supports 5, is driven through a sprocket 6 onthe conveyor belt roll 8, a chain drive i9, and another sprocket |2 onthe reel 4. The speed of the reel 4 is controlled by limit switches Mand H or their equivalent, through a magnetic clutch and brake, notshown, interposed between the sprocket l2 and the reel 4, in order thatthe veneer strip 2 may be automatically fed to the conveyor belt 2|without undue tensioning or piling up of the veneer. Although the veneerstrip is shown as unwinding from the forward side of the reel 4, it maybe unwound from the other side in opposite direction by reversing thereel drive and relocating the limit switches l4 and IS.

The conveyor belt 2|, which carries the veneer strip through the dryingchamber 21, is an endless wire mesh belt and is driven by a sprocket 22mounted on head shaft 24 which is supported in suitable bearings (notshown) carried by the frame 3. Power is supplied to head shaft 24 frommotor 10, through speed variator H and chain drive 12. At the infeed endof the drying chamber, the conveyor belt is supported by sprockets Iwhile the top and bottom flights of the conveyor belt are supported by aseries of idler rolls 9 attached to the frame 3 of the conveyor.

The drying chamber 21 is formed by insulated walls 29 and roof 28 withapertures 30 provided in each end wall through which the conveyor belt2| can enter and leave the chamber with the ribbon of veneer supportedand carried on its top flight. Hot air is circulated through the chamberand is directed against the top and bottom surfaces of the ribbon ofveneer.

In the preferred form of apparatus, controlled longitudinal tensionuniformly across the entire width of the continuous moving strip ofveneer is caused to develop during drying by providing an open meshapron 23, which lies on top of the continuously moving strip of veneer,said apron being attached to a transversely extending member 25 at theinfeed end of the dryer chamher and extending substantially the entirelength of the dryer chamber. For some operations, particularly withthick veneer, it may be desirable to operate the conveyorintermittently. Holddown rolls 3|, 32, 34 and 51 are provided to permitadjustment of the resistance of the apron to the transverse-grainshrinkage of the veneer. The hold-down rolls are journalled in pairs ofarms 4|, 43, 45 and 5| supported on pairs of supports 46, 41, 48 and 55attached to the frame 3 of the apparatus. An extension 40, 42, 44 and 52of roll-carrying arms 4|, 43, 45 and 5| is positioned between pairs ofopposed springs and 31, each backed up by an adjusting screw 39. Bymeans of said adjusting screws 39 through springs 35 and 31 the pressureexerted byrolls 3 32 and 34 on the apron 23 and by roll 5'! on theveneer strip 2 is individually adjustable to provide for progressivelyincreasing tension in the veneer strip, as is preferred. Another methodof adjusting the pressure on the veneer strip 2 is by the use of anoverlying apron of adjustable length, or by varying the effective weightof such overlying apron. 7 Though an overlying apron is used in thepreferred form of apparatus to increase the ease of feeding the forwardedge of a veneer strip through the dryer chamber and to provideincreased restraint on the thin veneer, particularly in view of the highair velocities commonly used in the dryer chamber, it will beappreciated that holddown rolls alone (though preferably more in numherthan shown), or other overlying means providing frictional resistance tothe forward movement of the veneer strip, can be employed to provide thenecessary tensioning of the veneer strip in accordance with ourinvention.

After the veneer strip has been dried to the desired moisture content,for example 5 to 10% (by weight on a dry basis), it passes out of thedryer chamber 21 and well beyond the end thereof, meanwhile cooling to asubstantial extent while still under tension due to hold-down roll 51and its associated adjusting mechanism. It is preferred to adjust thepressure of the final holddown roll 5'! so that there is little or noslippage between the conveyor belt 2| and the veneer strip 2 at thispoint, thus maintaining tension of the veneer strip during such coolingthereof. A considerable distance, which may be as long as twenty tothirty feet, is provided between the dryer chamber 2'! and the finalhold-down roll 51 for the dual purpose of permitting the veneer strip tocool and of allowing the operator to observe the continuously movingstrip of dry veneer after it leaves the drying chamber, regulate itsspeed to maintain the optimum dryness, and to make decisions as to wherethe continuously moving veneer strip should be severed to yield themaximum value in finished sheets of random or predetermined sizes inview of the defects such as knots which are commonly present in a ribbonof veneer.

Preferably, immediately after the dry veneer strip passes under thefinal tensioning roll 51, the operator cuts the continuously movingveneer strip into individual parallel-edged sheets with the drop-knife59 and associated apparatus, indicated generally at 60, in order toremove the defective portions from the dry veneer strip by clippingbefore further cooling of the veneer in the untensioned state causeswarping because of such defects, and at the same time provide means forcontinuously disposing of the output of the dryer.

The drop-knife apparatus 60 may be provided with a control device, whichin synchronism with the rate of discharge from the dryer will permit theoperator to implement his decision and cause the clipper knife todescend and sever the dry veneer strip into individual sheets ofpredetermined sizes of maximum value.

The individual dry veneer sheets are then removed by a conveyor, notshown, to grading and final inspection stations.

In a typical commercial installation, the distance between the firsthold-down roll 3| and the last hold-down roll 51 may be sixty feet ormore. Commercial rotary-cut birch veneer shrinks across the grain anaverage of 6.0% of the length of the strip of ribbon when dried to51-10% moisture content, which in sixty feet of veneer strip lengthwould be approximately 43 inches. If the pressure of the hold-down rolls3|, 32, 34 and 51 is such that there is no slippage of the veneer stripin respect to the conveyor belt, then the ribbon of veneer when driedwould have to stretch approximately 43 inches or the tension created bythe shrinkage will tear or split the ribbon of veneer apart in one ormore places. The usual species of wood cut into commercial rotary veneerwill not, under normal conditions, stretch transversely of the grain6.0% without tearing. Hence, the hold-down rolls 3|, 32 and 34 areadjustedto provide such a degree of tension that will not tear theveneer but will still reduce the shrinkage of the veneer strip to aconsiderableextent. For example, green birch veneer of thickness has anaverage tensile strength across the grain of 20 lbs. per inch of widthof strip; birch veneer of 1%. thickness averages 32 lbs.; birch veneerof thickness average46 lbs, and birch veneer of /6 thickness averagesj8llbs. Accordingly, these thicknesses of green birch veneer can'be driedunder a maximum tension which does not exceed these values.

Fig. 2'illustrates the reduction in shrinkage loss obtained by dryingindividual sheets of such green veneer under tension in a testapparatus,

and indicates the increase in output of veneer that can be obtained inthe commercial dryer by tensioning the veneer strip and thus reducingits shrinkage. Since a green veneer strip being dried by the method ofour invention is constantly moving, it is difficult accurately tomeasure directly the tension developed in the veneer strip during dryingand cooling. However, we believe the tension to be of the order of 100lbs. in the case, for example, of a continuous strip of veneer of' /gg"thickness and measuring 8' lengthwise of the grain, i. e., widthwise ofthe strip. As wood veneer is a natural product, .it is not uniform, andhence the drying tension, as a practical matter, must be substantiallyless than the tensile strength of the veneer strip. We prefer to adjustthe weight of the apron overlying the veneer strip to permit a reductionin shrinkage loss of approximately 1%. Comparison of such a reduction inshrinkage loss value to the curve of Fig. .2indicates a tension ofapproximately 30 lbs. per sq. inch, or approximately 100 lbs. totaltension in a continuous 8' veneer strip.

Fig. 3 .illustrates the curves of Fig. 2 as extended to includes theaverage tensile strength of dry birch veneer. Though we prefer to use atension in the veneer strip of approximately 30 lbs. per sq. inch acrossthe grain, tension between afew pounds and approximately 150 pounds persq; inch across the grain will serve for birch veneer. Since an averagetensile strength across the grain of dry birch is 980 lbs. per sq. inch,the above tension values indicate that a veneer strip may be tensionedadvantageously from as low as 0.33% to even as high as of the averagetensile strength across the grain of the veneer being'dried. It'isbelieved desirable, however, to operate in the range of OHS-4.5%, andpreferably in the range of 2.0-3.0%.

Although our invention has been described in connection with birchveneer as an example, other species of veneer may be dried by the methodand apparatus of our invention by the use of tensions of the percentagesof those above set forth;

This application is a continuation-in-part of our co pendingapplication, Ser. No. 526,730, filed March 16, 1944, for Apparatus forMaking Veneer, now abandoned, the subjectmatter of said priorapplication being incorporated in this application together withadditional subject matter.

We claim:

1. A method for drying wood veneer, including continuously conveyingtransversely to the grain of said veneer a strip of green veneer ofconsiderable length,'drying said strip and while drying maintaining itunder controlled tension suflicient to prevent substantial warping ofthe strip as it is being dried and insufiicient to cause destructivestress as the strip shrinks during drying and progressively increasingthe tensionoi the strip as it is being dried whileconveying and directlysupporting said strip from underneath substantially throughout itslength during drying.

2. A method for drying wood veneer, including continuously conveyingtransversely to the grain of said veneer a strip of green veneer ofconsiderable length, drying saidstrip and while drying maintaining itunder controlled tension sufiicient to prevent substantial warping ofthe strip as it is being dried and insufiicient to cause destructivestress as the strip shrinks during drying while conveying and directly,supporting said strip from underneath substantially throughout itslength during drying, and cooling said strip while maintaining tensionthereon.

3. A method for drying wood veneer, including continuously conveyingtransversely to the grain of said veneer a strip of green veneer ofconsiderable length, drying said strip and while drying maintaining itunder controlled tension suificient to prevent substantial warping ofthe strip as it is being dried and insufficient to cause destructivestress as the strip shrinks during drying and progressively increasingthe tension of the strip as it is being dried while conveying anddirectly supporting said strip from underneath substantially throughoutits length during drying, cooling said strip while maintaining tensionthereon, releasing the tension on said strip and thereafter cutting saidstrip into individual dried sheets.

4. The method of continuously making finished Wood veneer from anaxially supported roll of green veneer which comprises directly andpositively but slackly unwinding and downwardly leading therefrom astrip of green veneer without exerting destructive tension on the stripas it leaves the roll and with the grain thereof at right angles to itslead from said roll, continuously conveying, drying and cooling as aflat sheet the strip thus unwound while carrying and directly supportingsaid sheet substantially throughout its length, exerting pressure on thesurfaces thereof to maintain the veneer as a smooth fiat sheet duringsaid conveyin dryingand cooling, controlling the unwinding of the stripfrom the roll in timed relation to the feeding of the strip through thedryer, and-then immediately following completion of the coolingoperation clipping to finished dimensions dry veneer elements from thecontinuously moving fiat strip.

5. Apparatus for use in making Wood veneer comprising a dryer, conveyormeansto support substantially throughout its length and to continuouslycarry through said dryer veneer in strip form with the grain thereof atright angles to the conveyor movement, means for driving said conveyor,means for controlling tension on the veneer as it is conveyed throughsaid dryer to exert sufficient tension thereon to preventsubstantialwarping thereof and insufficient tension to cause destructive stress,said means including veneer overlying means providing'flexiblediscontinuous veneer contacting portions in frictional contactwith said veneer andmeans for varying the frictional resistance of saidcontacting portions on said veneer.

6. Apparatus for use in making wood veneer comprising a dryer, conveyormeans to support substantially throughout its length andto continuouslycarry through said dryer veneer in strip form with the grain thereof atright angles to the conveyor movement, means for driving said conveyor,means for controlling tension ontheveneer as it is conveyed through saiddryer :to exert sufficient tension thereon to prevent warping thereofand insuflicient tension to cause destructive stress, said meansincluding an overlying apron in'frictional contact with said veneer andmeans for varying the frictional resistance of said apron on saidveneer.

7. Apparatus for use in making veneer comprising a dryer, belt conveyormeans to support substantially throughout its length and to continuouslycarry through said dryer veneer in strip form with the grain thereof atright angles to the conveyor movement, means for driving said beltconveyor means, means for holding said veneer down upon said beltconveyor means to maintain the veneer as a smooth sheet thereon duringdrying thereof, dryer feeding means, roll supporting means adjacent theinfeed end of said dryer to support vertically spaced from said dryerfeeding means a roll of green veneer so that it may unwind slackly uponsaid dryer feeding means and be carried through said dryer in sheet formby said conveyor means, and power means arranged and controlled torotate directly the roll of green veneer when positioned in said rollsupporting means to unwind and feed the green veneer strip withoutexerting destructive tension thereon to said belt conveyor means intimed relation thereto to'provide a substantially uniform and continuousfeed of the strip through said dryer.

8. Apparatus for use in making veneer comprising a dryer, belt conveyormeans to support substantially throughout its length and continuouslycarry veneer through said dryer as a fiat sheet veneer in strip formwith the grain thereof at right angles to the conveyor movement, meansfor driving said belt conveyor means, means for holding said veneer downupon said belt conveyor means to maintain the veneer as a smooth flatsheet thereon during drying thereof, dryer feeding means, rollsupporting means adjacent the infeed end of said dryer to support a rollof green veneer vertically spaced from said dryer feeding means so thatit may unwind in a catenary upon said dryer feeding means and be carriedthrough said dryer in flat sheet form by said conveyor means, and powermeans arranged and controlled to rotate directly the roll of greenveneer when positioned in said roll supporting means to unwind and feedthe green veneer strip without exerting destructive tension thereon tosaid belt conveyor means in timed relation thereto to provide asubstantially uniform and continuous feed of the strip through saiddryer.

9. Apparatus for use in making veneer comprising a dryer, belt conveyormeans to support substantially throughout its length and to continuouslycarry through said dryer as a flat sheet veneer in strip form with thegrain thereof at right angles to the conveyor movement, means fordriving said belt conveyor means, means for holding said veneerdown'upon said belt conveyor means to maintain the veneer as a smoothflat sheet thereon during drying thereof, roll supporting means adjacentthe infeed end of said dryer to support above the infeed end of saidconveyor means a roll of green veneer so that it may unwind in acatenary and be carried through said dryer in fiat sheet form,'and powermeans arranged and controlled to rotate directly the roll of greenveneer when positioned in said roll supporting means to unwind and feedthe green veneer strip without exerting destructive tension thereon tosaid belt conveyor means in timed relation thereto to provide asubstantially uniform and continuous feed of the strip through saiddryer.

10. Apparatus for use in making wood veneer comprising a dryer, conveyormeans to support substantially throughout its length and to continuouslycarry through said dryer veneer in strip form with the grain thereof atright angles to the conveyor movement, means for driving said conveyormeans, means for holding said veneer down upon said conveyor, dryerfeeding means, roll supporting means adjacent the infeed end of saiddryer to support a roll of green veneer vertically spaced from anunderlying conveyor so that it may unwind in a catenary upon saidunderlying conveyor and be carried through said dryer in flat sheet formby said conveyor means, power means arranged and controlled to rotatethe roll of green veneer when positioned in said roll supporting meansto unwind and feed the green veneer strip without exerting destructivetension thereon to said belt conveyor means in timed relation thereto toprovide a substantially uniform and continuous feed of the strip throughsaid dryer, veneer cooling means including conveyor means to supportsubstantially throughout its length and to continuously carry saidveneer in strip form, means to maintain tension in the veneer stripduring cooling thereof, and cutting means arranged and controlled to outsaid veneer strip into dried individual sheets immediately upon releaseof tension on said veneer strip.

11. The method of continuously making finished wood veneer from anaxially supported roll of green veneer which includes the steps ofslackly unwinding and leading therefrom a strip of green veneer withoutexerting destructive tension on the strip as it leaves the roll and withthe rain thereof at right angles to its lead from the roll, drying saidstrip and while drying maintaining it under controlled longitudinaltension uniformly across the entire width of the strip sufficient toprevent substantial warping of the strip as it is being dried andinsuflicient to cause destructive stress as the strip shrinks duringdrying while conveying and directly supporting the strip from underneathsubstantially throughout its length during drying.

12. An apparatus as set forth in claim 6 further including means forcooling said veneer while it is under controlled tension.

13. An apparatus as set forth in claim 6 further including cutting meansarranged and controlled to out said dried veneer strip into driedindividual sheets.

14. A method for drying wood veneer, including continuously conveyingtransversely to the grain of said veneer a strip of green veneer ofconsiderable length, drying said strip and while drying maintaining itunder controlled longitudinal tension uniformly across the entire widthof the strip sufficient to prevent substantial warping of the strip asit is being driedand insufficient to cause destructive stress as thestrip shrinks during drying while conveying and directly supporting saidstrip from underneath substantially throughout its length during drying.

15. A method for drying wood veneer, including continuously conveyingtransversely to the grain of said veneer a strip of green veneer ofconsiderable length, drying said strip and while drying maintaining itunder controlled longitudinal tension uniformly across the entire widthof the strip sufficient to prevent substantial warping of the strip asit is being dried and insuflicient to cause destructive stress as thestrip shrinks during drying while conveying and directly supporting saidstrip from underneath substantially throughout its length during drying,releasing the tension on the dried strip and thereafter cutting thestrip into individual dried sheets.

LANGDON C. QUIMBY. ALLEN QUIMBY, JR.

10 REFERENCES CITED The following references are of record in the fileof this patent:

5 UNITED STATES PATENTS Number Name Date 1,573,379 Eimendorf Feb. 16,1926 1,578,020 Elmendorf Mar. 23, 1926 1,642,928 Kocha Sept. 20, 1927 101,969,712 Heifirich Aug. 7, 1934

